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Chlamydomonas inner-arm dynein mutant, ida5, has a mutation in an actin-encoding gene.

Kato-Minoura T, Hirono M, Kamiya R - J. Cell Biol. (1997)

Bottom Line: These mutants were found to have mutations in the conventional actin gene, such that its product is totally lost; ida5 has a single-base deletion that results in a stop codon at a position about two-thirds from the 5' end of the coding region, and ida5-t lacks a large portion of the entire actin gene.The net growth rate of ida5 and ida5-t cells did not differ from that of wild type, but the mating efficiency was greatly reduced.These results suggest that NAP can carry out some, but not all, functions performed by conventional actin in the cytoplasm and raise the possibility that Chlamydomonas can live without ordinary actin.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, School of Science, Nagoya University, Japan.

ABSTRACT
Chlamydomonas flagellar inner-arm dynein consists of seven subspecies (a-g), of which all but f contain actin as subunits. The mutant ida5 and a new strain, ida5-t, lack four subspecies (a, c, d, and e). These mutants were found to have mutations in the conventional actin gene, such that its product is totally lost; ida5 has a single-base deletion that results in a stop codon at a position about two-thirds from the 5' end of the coding region, and ida5-t lacks a large portion of the entire actin gene. Two-dimensional gel electrophoresis patterns of the axonemes and inner-arm subspecies b and g of ida5 lacked the spot of actin (isoelectric point [pI] = approximately 5.3) but had two novel spots with pIs of approximately 5.6 and approximately 5.7 instead. Western blot with different kinds of anti-actin antibodies suggested that the proteins responsible for the two novel spots and conventional actin are different but share some antigenicity. Since Chlamydomonas has been shown to have only a single copy of the conventional actin gene, it is likely that the novel spots in ida5 and ida5-t originated from another gene(s) that codes for a novel actin-like protein(s) (NAP), which has hitherto been undetected in wild-type cells. These mutants retain the two inner-arm subspecies b and g, in addition to f, possibly because NAP can functionally substitute for the actin in these subspecies while they cannot in other subspecies. The net growth rate of ida5 and ida5-t cells did not differ from that of wild type, but the mating efficiency was greatly reduced. This defect was apparently caused by deficient growth of the fertilization tubule. These results suggest that NAP can carry out some, but not all, functions performed by conventional actin in the cytoplasm and raise the possibility that Chlamydomonas can live without ordinary actin.

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Mating efficiency. (Ordinate) Percentage of cells that  underwent cell fusion and became quadriflagellate. (Abscissa)  Time after the onset of mating. The combinations of mating pairs  are shown with a slash. + and − denote the mating type of the gametes used. Since the flagella of zygotes were gradually resorbed  with time, the apparent mating efficiency decreased after ∼2 h of  mating.
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Figure 6: Mating efficiency. (Ordinate) Percentage of cells that underwent cell fusion and became quadriflagellate. (Abscissa) Time after the onset of mating. The combinations of mating pairs are shown with a slash. + and − denote the mating type of the gametes used. Since the flagella of zygotes were gradually resorbed with time, the apparent mating efficiency decreased after ∼2 h of mating.

Mentions: During the sexual conjugation of Chlamydomonas, mt+ gametes produce a process of a few micrometers in length at the apical end of the cell body and thereby facilitate the cell fusion process (Goodenough and Weiss, 1975). This process, called the fertilization tubule, has been shown to contain an F-actin bundle (Detmers et al., 1983). We speculated that ida5 gametes may be deficient in fertilization because they cannot produce the fertilization tubule normally. Just as we expected, the efficiency of cell conjugation greatly decreased when mt+ ida5 was mated with mt− wild type or ida5. Interestingly, conjugation efficiency did not decrease when mt− ida5 was mated with mt+ wild type (Fig. 6). These results suggest that the gamete of mt+ ida5 is deficient in fertilization tubule growth.


Chlamydomonas inner-arm dynein mutant, ida5, has a mutation in an actin-encoding gene.

Kato-Minoura T, Hirono M, Kamiya R - J. Cell Biol. (1997)

Mating efficiency. (Ordinate) Percentage of cells that  underwent cell fusion and became quadriflagellate. (Abscissa)  Time after the onset of mating. The combinations of mating pairs  are shown with a slash. + and − denote the mating type of the gametes used. Since the flagella of zygotes were gradually resorbed  with time, the apparent mating efficiency decreased after ∼2 h of  mating.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139884&req=5

Figure 6: Mating efficiency. (Ordinate) Percentage of cells that underwent cell fusion and became quadriflagellate. (Abscissa) Time after the onset of mating. The combinations of mating pairs are shown with a slash. + and − denote the mating type of the gametes used. Since the flagella of zygotes were gradually resorbed with time, the apparent mating efficiency decreased after ∼2 h of mating.
Mentions: During the sexual conjugation of Chlamydomonas, mt+ gametes produce a process of a few micrometers in length at the apical end of the cell body and thereby facilitate the cell fusion process (Goodenough and Weiss, 1975). This process, called the fertilization tubule, has been shown to contain an F-actin bundle (Detmers et al., 1983). We speculated that ida5 gametes may be deficient in fertilization because they cannot produce the fertilization tubule normally. Just as we expected, the efficiency of cell conjugation greatly decreased when mt+ ida5 was mated with mt− wild type or ida5. Interestingly, conjugation efficiency did not decrease when mt− ida5 was mated with mt+ wild type (Fig. 6). These results suggest that the gamete of mt+ ida5 is deficient in fertilization tubule growth.

Bottom Line: These mutants were found to have mutations in the conventional actin gene, such that its product is totally lost; ida5 has a single-base deletion that results in a stop codon at a position about two-thirds from the 5' end of the coding region, and ida5-t lacks a large portion of the entire actin gene.The net growth rate of ida5 and ida5-t cells did not differ from that of wild type, but the mating efficiency was greatly reduced.These results suggest that NAP can carry out some, but not all, functions performed by conventional actin in the cytoplasm and raise the possibility that Chlamydomonas can live without ordinary actin.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, School of Science, Nagoya University, Japan.

ABSTRACT
Chlamydomonas flagellar inner-arm dynein consists of seven subspecies (a-g), of which all but f contain actin as subunits. The mutant ida5 and a new strain, ida5-t, lack four subspecies (a, c, d, and e). These mutants were found to have mutations in the conventional actin gene, such that its product is totally lost; ida5 has a single-base deletion that results in a stop codon at a position about two-thirds from the 5' end of the coding region, and ida5-t lacks a large portion of the entire actin gene. Two-dimensional gel electrophoresis patterns of the axonemes and inner-arm subspecies b and g of ida5 lacked the spot of actin (isoelectric point [pI] = approximately 5.3) but had two novel spots with pIs of approximately 5.6 and approximately 5.7 instead. Western blot with different kinds of anti-actin antibodies suggested that the proteins responsible for the two novel spots and conventional actin are different but share some antigenicity. Since Chlamydomonas has been shown to have only a single copy of the conventional actin gene, it is likely that the novel spots in ida5 and ida5-t originated from another gene(s) that codes for a novel actin-like protein(s) (NAP), which has hitherto been undetected in wild-type cells. These mutants retain the two inner-arm subspecies b and g, in addition to f, possibly because NAP can functionally substitute for the actin in these subspecies while they cannot in other subspecies. The net growth rate of ida5 and ida5-t cells did not differ from that of wild type, but the mating efficiency was greatly reduced. This defect was apparently caused by deficient growth of the fertilization tubule. These results suggest that NAP can carry out some, but not all, functions performed by conventional actin in the cytoplasm and raise the possibility that Chlamydomonas can live without ordinary actin.

Show MeSH
Related in: MedlinePlus